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In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge

Forsyth, C; Fazakerley, AN; Rae, IJ; Watt, CEJ; Murphy, K; Wild, JA; Karlsson, T; ... Zhang, Y; + view all (2014) In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge. JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS , 119 (2) 927 - 946. 10.1002/2013JA019302. Green open access

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Abstract

The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100 km at altitudes of 4000–7000 km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120–240 s after Cluster 4 at 1300–2000 km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction, in contrast to the expected east-west orientation of the preonset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF-driven “wedgelets.” Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW.

Type: Article
Title: In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge
Open access status: An open access version is available from UCL Discovery
DOI: 10.1002/2013JA019302
Publisher version: http://dx.doi.org/10.1002/2013JA019302
Additional information: ©2014. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Keywords: Substorm current wedge, Field-aligned current, Wedgelets, Aurora, Magnetosphere, Earth
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/1418105
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